Technical Terms related to a lens
centre of curvature
radius of curvature
principal axis
optical centre
the centre of the sphere whose part is the lens surface
the radius of the sphere whose part is the lens surface is called radius of curvature of that surfac of the lens
for thin lens radius of curvature of a surface of lens is = to the distance of the centre of curvature of that surface from the optical centre
the line joining the centre of the curvature of 2 surfaces of the lens
It is a point on the principal axis of the lens such that a ray of light passing through this point emerges parellel to its direction of incidence
It is the centre of lens
optical centre of a thin lens is the point on principal axis of a lens such that ray of light directed towards it passes undeviated through it
first focal point
it is a point F1 on the principal axis of the lens the rays of light coming from it after refraction through lens becomes parellel to principal axis
second focal point
concave lens- the incident rays of light apperaing to meet at it after refraction from lens become parellel to principal axis of the lens
it is the point F2 on the principal axis of the lens such that the rays of light incident parellel to principal axis
the rays of light incident parellel to principal axis after refraction from lens appear diverging from this point
Focal plan
a plan normal to the principal axis passing through the focus
first focal plane
secound focal plane
a plane passing through the first focal point and normal to the principal axis on the lens
a plane passing through the secound focal point and normal to the principal axis of the lens
focal length
the distance of focus from optical length
first focal length
second focal length
the distance from the optical centre O of the lens of its first focal length
the distance from the optical centre O of the lens to the second focal point F2